In manufacturing plants it is customary to transport equipment, such as machine loading devices, pallets, and robots, from one location to another. Where the equipment is shuttled between two locations positioned on a simple geometric path, linear slides or rotating tables are normally used. Typically, conveyors, belts, and link chains are utilized for longer travel and for negotiating winding paths around other machines and equipment. Furthermore, automatically guided vehicles, AGV's, have the capability to trace guide wires, or markings on, or within, a shop floor allowing greater mobility and eliminating the need for guide structure on the shop floor.
AGV's can also cover considerable distances and can have the ability to be programmed to trace variable paths depending on material routing requirements. Computer control systems provide the capability to communicate along the guide wires, or wirelessly, with central plant computers to receive route commands. AGV systems require sophisticated control systems on-board the AGV as well as at a central location that coordinates their motion. They also require an on-board power source, usually batteries, to propel them between loading stations. A power distribution system is also necessary to re-charge the batteries at loading stations by means of a plug and socket arrangement. The flexibility and extensive mobility of AGV systems is reflected in their cost and often makes them too expensive for many applications requiring limited mobility.
The high level of sophistication of the AGV control and guidance systems, which involves advanced sensing technologies, makes their maintenance and operation also a challenge for many enterprises, and well outside the capability of many potential users. The need is well recognized for a simple, low cost, transporting device and location method that supports equipment relocation requirements when limited mobility is sufficient.
AGV's also have a problem of not providing accurate position or height location for the transported equipment. This is particularly significant if robots are transported and are programmed to operate with a high level of accuracy at several locations.
Prior art references noted by a search conducted prior to filing this application are discussed below.
U.S. Pat. Nos. 128,178 to Sells; 1,229,954 to Hedges; 1,682,717 to Corona; and 2,941,481 to Philbrick disclose various motor driven vertically disposed linkages for propelling supported vehicles. These patents teach the conversion of rotation in a horizontal plane into displacement of linkages in a vertical plane.
U.S. Pat. No. 4,558,758 to Littman et al discloses a mobile robot having a central body and legs with wheels which allow movement both up and down as well as sideways.
U.S. Pat. No. 4,790,400 to Sheeter discloses a stepping vehicle that uses at least two sets of telescopically extendable legs that are mounted on a work platform for translational movement. The vehicle can "walk" by controlling the telescopic extension of the legs while at the same time controlling the translational movement of the legs with respect to the work platform.